Presentation of Paper CPA-033- 2008.pdf - Pavement Engineering ...

Improved Performance 

Evaluation of Road Pavements by 

Using Measured Tyre Loading 

James Maina and Morris De Beer 

CSIR Built Environment, South Africa

Paper today: “Improved Performance Evaluation of Road 

Pavements by Using Measured Tyre Loading” 

• Part 1: 

• General introduction; 

• Quality and importance of road infrastructure in SA; 

• Trucks on our road infrastructure; 

• Truck tyre loading and stresses; 

• Stress-In-Motion (SIM) Technology; 

• Typical Stress-In-Motion (SIM) Data; 

• Part 2: 

• Equations for mechanistic road analysis; 

• Analysis for multiple loading; 

• Strain Energy of Distortion (SED); 

• Worked Examples and Analytical Results; 

• Summary of research findings; 

• Recommendations. 

© CSIR 2008 www.csir.co.za

SOUTH AFRICAN 

MAJOR PAVED 

ROAD NETWORK 

~ 20 000 km 


Background… 

• SA: 750 000 km of roads - 20 % paved; 

• Road Pavement Engineering critical for upgrade & 

sustainability of road infrastructure; 

• Locally developed Stress-In-Motion (SIM) study part 

of this process; 

• Analytical: Strain Energies of Distortion (SEDs) at 

various sections within the road pavement 

structure were determined – good promise !; 


7 700 km National 

Roads in SA of 

Freeway/Expressway 

standard 


Freight Transport in SA….(CSIR - 4 th 

Logistics Report, 2007). 

th SA 

• The 4 th annual State of Logistics Survey for SA 

indicated that total land transport accounted for 

1,5 billion tonnes, with recent growth of higher 

than 5 per cent, mainly captured by the road 

transport sector, as opposed to the rail sector 

carrying only 0.2 billion tonnes. 


Freight Transport in SA….(CSIR - 4 th 

Logistics Report, 2007). 

th SA 

Figure 1. Historical freight transport data (CSIR, 2007). 


Traffic Volumes and Road Damage…. 

• Traffic volumes on our national highways are at all 

time highs, for example, N3 has already carried 

the equivalence of 20 years of traffic over the 

last two years. (..2007..) 

•Daily, newspapers carry articles on potholes and 

other road shortcomings which cost motorists in 

excess of R200 billion a year (News24, 2008). 

It is therefore not surprising that there have been numerous calls 

for extensive revision of important parts of the SA road pavement 

design method in order to cope with the new traffic realities, 

amongst other factors. 


Heavy Vehicles…. 


Growth in Heavy Vehicle (HV) Traffic… 

• In terms of growth in HVs on the toll portion of the 

road, the rate was approximately 8 per cent 

since 2002-2007, 2007, 20 per cent 2006-2007, and 

almost 40 per cent between February and 

October 2007. 

• The N3 is therefore the national road with the 

highest growth and HV composition in SA (Le 

Roux, 2007). 


More Specific issues in Paper today… 

• South African Roads, Trucks @ Road Damage; 

• Introduction into Stress-In-Motion (SIM) technology; 

• Tyre Studies with Heavy Vehicle Simulator (HVS); 

• Full Scale SIM Testing @ N3-Traffic Control Centre 

(TCC) -Heidelberg, SA @ typical SIM Results; 

• Implications for Road Surface Design and Road 

Preservation/Protection – Analytical Evaluations.. 

• Summary, Conclusions and Recommendations 


Vehicle-Tyre-Pavement Interaction: 

STRESS-IN-MOTION (SIM) 

Technology 


Thin Asphalt Surfacings (30 mm to 50 mm) on 

crushed rock: Economical in dry regions. 


From: http://www.i-traffic.co.za/index.phpq=cameras 

At Buccleuch 

2008/11/13; 17:05:40 

North of Buccleuch facing South 

2008/11/13; 17:05:40

Truck Tyre Inflation Pressure in South Africa 

~ 20 % 

Increase 

in 

20 Years 


Road Damage…. 


Longitudinal Flow of Asphalt 

Fatigue Cracking and aging 

Delamination.. 

EXAMPLES OF ROAD SURFACE FAILURES.. 


Tyres and Road Structures….. 

…from SANRAL: www.nra.co.za

Modern Tyre science… 

”Sectometer” 

S. Eckens, 1928 


Gautrans Heavy Vehicle Simulator (HVS) Mark IV+: 

Loading Device for Controlled loading tests on roads.. 


LOADS & STRESSES FROM TYRES: 


425 /65 R22.5 HVS TYRE ON SIM SYSTEM 


Stress-In-Motion testing with HVS 

Dual Load Configuration – Twin SIM pads 


STRESS-IN-MOTION TESTING USING THE HVS 


TYRE DEFLECTION & TYRE PRINTS… 


TYRE DEFLECTION & TYRE PRINTS… 

315/80 R22.5 HVS Tyre: 

Overloaded 


Overloading on Tyres….and contact with road.. 

Tyre Contact Patches: 

(square not circular)… 


Assumption of Tyre Loading - Pavement Design 

Modeling: 

- Circular; 

- Variable Vertical load; 

- Variable pressure, 

but UNIFORM & 

No Shear Forces 

included. 

Tyre Loading, P (kN) 

Uniform Contact Stress, q (kPa) 


Dual Tyre: 3D-Contact Stresses (Pressure)… 

Stress 

Ratio: 

10:3:1 


Typical SIM 3D Data Sets - Variable loading: 

3D – Z,X,Y - 

Contact Stresses: 

Variable loads: 

315/80 R22.5 Tire 


TYRE LOAD 

TYRE “FINGER PRINTING”: (11R22.5 TYRE)… 

TYRE INFLATION PRESSURE 


Truck Weighing - National Road 3 (N3), near Heidelberg 

in Gauteng…. 


QUAD SIM PAD TESTING AT WEIGH-BRIDGE SITE: 

N3 NORTH – HEIDELBERG TRAFFIC CONTROL CENTRE 

4 x SIM Scales 


Quad (full) SIM pad configuration at a typical 

weighbridge site on National Road 3 (N3), near 

Heidelberg in Gauteng 


Examples of Stress-In-Motion (SIM) Testing on the 

N3 – Freeway near Heidelberg…. 


Quad (full) SIM pad configuration at a typical weighbridge site on 

National Road 3 (N3), near Heidelberg in Gauteng 


Quad (full) SIM Scale on National Road 3 (N3), near 

Heidelberg in Gauteng …. 


SIM Measurement: N3- “1232” Tanker… 


SIM In operation – N3-TCC ……. 


STATIC & DAW 50 Scales (Tonne) 

SIM Scales: Accuracy checking @ N3-TCC… 

D:\ICAP-2006\[MODIFIED-2SEPT-17OCT-ICAP-2006.xls]Total Load-GVM-GCM- 

SIM vs MULTI-DECK STATIC AND DAW 50 at N3-TCC (Heidelberg) (GVM/GCM) 

STATIC (1861) DAW50 (1501) Line of Equality Linear (STATIC (1861)) Linear (DAW50 (1501)) 

70 

65 

60 

55 

50 

45 

40 

35 

30 

25 

20 

15 

10 

5 

0 

STATIC = 1.0025 x SIM 

(n = 1 245), R 2 = 0.99; 

Std. Y-Error: 1.37 Tonne; 

Std. Error (Coef) : 

0.0001. 

DAW 50 = 0.9931 x SIM 

(n = 1 245), R 2 = 0.99; 

Std Y-Error: 1.42 Tonne; 

Std. Error (Coef): 

0.00011. 

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 

SIM (Tonne) 


Normalised Frequency 

Tyre Inflation Pressure Distributions – N3- 2003 

1.2 

H:\CAPSA04\[Tyre Inflation Pressure Information-MORTON-MDB- 

N3 TCC - SELECTED HEAVY VEHICLE (HV) TRUCK TYRE PRESSURE DATA 

(26 Feb 2003 - 06 March 2003) 

LEFT-FRONT-(225 tyres) RIGHT-FRONT-(225 tyres) REST-LEFT-(845) REST-RIGHT-(845) 

1 

0.8 

0.6 

0.4 

0.2 

0 

0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 

TYRE INFLATION PRESSURE (kPa) 


Number of Trucks 

Gross Vehicle Mass (GVMs)……. 

GVM/GCM-SIM N3 TCC - 2003 

RESULT RATINGS 1 AND 2 (n = 2 297) 

[2 Sept - 17 Oct 2003] 

250 

225 

200 

175 

150 

125 

100 

75 

50 

25 

0 

1.000 

4.000 

15 Tonne 

29 Tonne 

7.000 

10.000 

13.000 

16.000 

19.000 

22.000 

25.000 

28.000 

31.000 

51 Tonne 

Bin: Vehicle Mass: GVM/GCM [Tonne] 

© CSIR 2008 www.csir.co.za 

34.000 

37.000 

40.000 

43.000 

46.000 

49.000 

52.000 

55.000 

58.000 

61.000 

64.000 

67.000 

70.000 

73.000 

76.000 

79.000 

82.000

Number of Tyres 

Axle Mass Distributions – N3- 2003 

H:\ICAP-2006 Summary N3 TCC-FINAL-4-B-ICAP-2006.xls TYRES-1-2 -Histogram-Paper (2) 

ALL TYRES MEASURED: n = 45 227 (This Study) - N3 -TCC-2003 

All Other Tyres Axle 1 Left Axle 1 Right 

1600 

All other 

Tyers: 

1.9 Tonne 

Steering 

Tyres: 

2.95 Tonne 

120 

1400 

100 

1200 

1000 

80 

800 

60 

600 

40 

400 

200 

20 

0 

0 

0.050 

0.300 

0.550 

0.800 

1.050 

1.300 

1.550 

1.800 

2.050 

2.300 

2.550 

2.800 

3.050 

3.300 

3.550 

3.800 

4.050 

4.300 

4.550 

4.800 

Bin: Tyre Mass Weight [Tonne] 


Vertical Stress Cumulative Frequency – N3- 2003 


Measured Tyre Foot Prints :Two Axle Truck – Vertical 

Contact Stress –….. 


4 Axle Truck…. 






Eight (8) Axle Truck – Vertical Contact 

Stress - Foot Prints…. 


Counts 

STEERING AXLE – UNEQUAL LOADING……. 

TEST 009: KTD 904 GP 13/10/2003: AXLE 1 

450 

185 mm; 1.938 Ton 

266 mm; 3.739 Ton 

400 

350 

300 

250 

200 

150 

100 

50 

10 20 30 40 50 60 70 80 

Across the SIM pads 


Counts 

UNEQUAL LOADING ON TRUCK TYRES…. 

TYRE BARELY IN CONTACT WITH SURFACE 

550 

500 

189 mm; 

0.037 Ton 

TEST 768-09/10/2003: DDT235N AXLE 2 

297 mm; 

4.312 Ton 

202 mm; 

1.874 Ton 

194 mm; 

1.223 Ton 

450 

400 

350 

300 

250 

200 

150 

100 

50 

10 20 30 40 50 60 70 80 



Counts 

AXLE 2: MISSING TYRE !! 

TEST 765: NKR 9519 - 09/10/2003 AXLE 2 

350 

244 mm; 

1.782 Ton 

196 mm; 

1.032 Ton 

195 mm; 

0.661 Ton 

300 

250 

200 

150 

100 

50 

10 20 30 40 50 60 70 80 



ANALYTICAL ROAD PAVEMENT MODEL…. 

Side view 

of tyre 

APPLIED LOAD/STRESSES 

P/σ 

P/σ 

End view 

of tyre 

Vertical, 

Longitudinal & 

Lateral 

3D Contact 

Stresses 

Stress 

Rotation 

Surfacing: h 1 , E 1 , v 1 

Pavement 

Response: 

Stresses 

& 

Strains 

Base 

Layer: 

h 2 , E 2 , v 2 

Subbase 

Layer: 

h 3 , E 3 , v 3 

Selected 

Layer: 

h 4 , E 4 , v 4 


Subgrade/ 

Foundation: 

h 5 , E 5 , v 5

General Features & Assumption 

• Pavement: Multilayer elastic system with a 

possibility of interface slip. 

• Surface load: Single/Multiple circular loads. 

• Analysis: Single/Multiple points of interest. 

• Response: Stresses, strains, and 

displacements 


Uniformly distributed circular load 

Vertical 

load 

Horizontal 

load 

vertical + 

horizontal loads 

surface 

Base 

Subgrade 


Stresses within a Road Pavement Structure 

- rz Axes - 

y 

Load 

 

z 

x 

r 

 

z r 

rz 

r 

z 


Stresses within a Road Pavement Structure.. 


Global Cartesian 

coordinate system 

Y 

load 

r 

Local Cartesian and 

cylindrical coordinates 

a 

 

x 

X 

y 

 

z 

r 

Stress acting on an element 

rz = zr 

z 

z = z 

z 

Z 

Arrows give 

directions for 

positive sign 

 

r = r 

r 


Multilayer Structural Model: 

Layer Modulus Poisson’s 

ratio 

h E 1 

n 1 

h i E i 

E n 

n i 

1 

h 

2 

h i-1 

E 2 

E i-1 

n 2 

n i-1 

n n 

(0, 0, 0) 

Y 

y 


2a 

r 

 

a 

X 

measurement 

point 

(X 0 +r Cos( +a), Y 0 +r Sin( +a), 0) 

x

Assumption of Tyre Loading - Pavement Design 

Modeling: 

- Circular; 

- Variable Vertical load; 

- Variable pressure, 

but UNIFORM & 

No Shear Forces 

included. 

Tyre Loading, P (kN) 

Uniform Contact Stress, q (kPa) 


SIM systems.. 


Rutting- Controlled testing with Heavy Vehicle 

Simulator (HVS)… 

Controlled Field Tests with HVS…on R80 route. 


Wide Base Single Tyre- Input Data: Vertical 

Stress Patterns: “n” and “m” – Shapes… 

“n – Shape” “m – Shape” 


Wide Base Single Tyre- Input Data: Vertical 

Stress Patterns: “n” and “m” – Shapes… 

“n – Shape” “m – Shape” 


Rutting- Controlled testing with Heavy Vehicle 

Simulator (HVS)… 


Vertical Tyre Stress: “n-Shape” tyre stress 

results in “n-Shape” rutting in asphalt overlay.. 


Vertical Tyre Stress: “m-Shape” stress result in 

“m-Shape” rutting in asphalt overlay.. 



distribution 


Strain Energy of Distortion (SED) on road 

surface: From “n” – Shape single tyre stress… 



distribution. 


Road Surface: Strain Energy of Distortion (SED) 

– from “n – Shape” single tyre stress… 


Road Surface: Strain Energy of Distortion (SED) 

– from “n – Shape” single tyre stress… 


Strain Energy of Distortion (SED)- “n” and ”m – 

Shape” - dual tyres..…. 


Strain Energy of Distortion (SED) – Dissipation 

with road pavement depth… 


1 x Truck - 30 Tyres: 1 mm x 1 mm resolution – 500k points – 

SED under Steering Axle …… 

50 mm AC layer 


…SED under Steering Axle 

50 mm AC layer 


Summary, Conclusions (1): 

• South African Roads, Trucks @ Road Damage – real 

cause of concern; 

• Tyre Studies with Heavy Vehicle Simulator (HVS); 

• Successful Demonstration - Stress-In-Motion (SIM) 

technology; 

• Analytic approach - SED shows good promise for 

further implementation; 

• Implications for Road Surface Design and Road 

Preservation/Protection – Important to be 

implemented; 

• SIM future of existing Weigh-In-Motion (WIM) . 


Summary, Conclusions (2): 

• The concept of SED as a response parameter that 

quantifies road pavement’s “potential for failure”: 

seems to resonate well with the applied tyre stresses 

and its different shapes. 

• Single wide base tyres induce more than double the 

potential for failure compared with the dual tyre 

configuration on the same road pavement. 

• Under-inflated-heavily-loaded loaded tyres may cause more 

damage on the surface of the road compared to 

correctly inflated tyres. 

• The combination of SIM technology and SED from 

numerical modelling may be used to identify areas of 

high potential for failure on the road pavement 

system. 


Conclusions- based on SED 

Evaluation:… 

• Depending on the shape of the vertical contact stress 

distribution, the damaging effect in terms of SED of 

the single tyre appears to be 2.0 to 4.3 times higher 

than dual tyres under the same total loading. 

• For both tyres, the damaging effect appears to be 

between 1.7 and 3.5 higher for the m-shape contact 

stress distribution. 

• The top 5 mm to 10 mm of road pavements is 

potentially more prone to failure (top-down cracking 

or rutting) than was perhaps realised in the past. 


Recommendations: 

• Further research work is needed to establish 

if this trend of tyre type is similar for all road 

pavement structures in South Africa before it 

is safe to argue against the use of single tyres 

vs dual tyres or make recommendation on 

tyre inflation pressure for HVs. 

• Implementing concept of SED in road design; 


Thank You for listening 

today……any Questions

Presentation of Paper CPA-033- 2008.pdf - Pavement Engineering ...

Create successful ePaper yourself

Delete template?

Save as template?